In a large bowl, combine vanilla frosting, peanut butter and margarine, until well blended. Stir in crumbs until well mixed. Form 1 inch balls; chill for 1 hour. In a small saucepan, melt chocolate frosting over low heat, stirring occasionally. Dip chilled balls in melted frosting; allow excess to drip off. Place on wire rack over waxed paper; let stand at room temperature until dry, about 6 hours.